My mom recently had a lung biopsy of a 2.5 cm mass in the left upper lobe all the biopsies came back benign. She then had a PET scan done 2 weeks later and the Physicians are now saying she has cancer and will need to have a thoracotomy or cyber knife to remove mass. I am having a problem understanding how one minute it's not cancer and the next minute it is cancer. Please help me here. Thank you